A technology disclosed herein relates to a computer system for operating a database (hereinafter, referred to as “DB”) and a storage system for storing data of the DB, in particular, a technique of reducing power consumption of a storage system.
There currently exist many different applications based on a DB, which makes it extremely important to employ a database management system (hereinafter, referred to as “DBMS”) for performing a series of processing/management involving the DB. One of the characteristics of the DB is handling an enormous amount of data. Therefore, in general, many computer systems in which a DBMS operates (hereinafter, referred to as “DB systems”) have such a system configuration that a computer on which a DBMS (hereinafter, referred to as “DB server”) runs is coupled to a storage system including a plurality of disk drives (in other words, having a large capacity) to store data of the DB in the storage system.
The data of the DB managed by the DBMS tends to be increasing year by year, which further increases in capacity of the storage system. As one of methods of increasing the capacity of a storage system, there is a method of increasing the number of installed disks. The increase in the number of installed disks leads to an increase in storage area, but the rotations of the disks consume more power. Therefore, the increase in the number of disks raises a problem in that power consumption of the entire storage system becomes larger. JP 2000-293314 A is known as an example of a technique for reducing the power consumption of the storage system.
JP 2000-293314 A discloses a technique of controlling power-saving conditions of disk drives (in other words, powering on/off and selection of a power-saving mode) if a disk array system does not receive an access request from a host system within a predetermined time. Upon reception of the access request from the host system, the disk array system turns on power of a disk drive to be accessed if the power thereof is off, and then executes the access.
From the viewpoint of a single disk (hard disk drive), the power consumption relates to an rpm of the disk. To be specific, the lower the rpm is, the lower the power consumption is, while the higher the rpm is, the higher the power consumption is. “ACM SIGARCH Computer Architecture News, Proceedings of the 30th annual international symposium on Computer architecture ISCA '03, Volume 31 Issue 2” discloses a technique of the disk capable of dynamically changing the rpm. According to this technique, it is possible to control the power consumption by setting the rpm of the disk to be low.
JP 2005-258735 A discloses a technique of improving performance of the DB system by causing the DBMS to read out data to be accessed from the disk of the storage system in advance based on a query plan created by the DBMS upon execution of a query, and to write the data into a cache memory. Such processing of reading data to be accessed from the disk in advance and holding the data in a memory is called “prefetch”.